Various types of travelling machinery such as cranes and gantries require accurately aligned rail supports for their proper operation. Rails which are not parallel or straight within acceptable tolerances lead to the shifting out of square of the travelling machine's frame, and to excessive wearing of rails and wheels. Due to the vibration caused by moving machinery, impact loads exerted upon the rails, and settlement or shifting of supporting structures, the rails may move out of accurate alignment. Periodic maintenance is required to check the alignment of rails and take corrective action to prevent damage or premature wear.
In order to enable accurate periodic realignment and initial alignment of rails, adjustable connecting devices have been developed. Generally, a rail is laid between opposing rows of connectors spaced at regular intervals along the length of the rail. The connectors are arranged in opposing pairs each clamping one side of the flange to the supporting surface. The spacing of the connector pairs is determined by the prevailing loads, the rail capacity and connector capacity.
Commonly, the connectors comprise a rail clip having an oversized or slotted hole through which a bolt passes. The clips have a forward portion extending over the rearward portion of the flange's top surface to engage and secure the flange in position. The bolt is fixed to the supporting surface at its lower end and has a threaded upper end to receive a mating nut and lock washer. When in a clamped condition, the clip is locked to the supporting surface by the nut and lock washer. A bearing-type connection is commonly used, wherein the design load capacity is determined by bearing between the bolt, washer and clip, rather than a friction-type connection. When in a loose condition, the nut is withdrawn upwardly and the clip is free to slide forwardly and rearwardly to the extent allowed by the bolt within the oversized or slotted hole. Between the bottom surface of the flange and the supporting surface, a resilient pad may be placed to reduce the effects of impact and vibration. Bolts of various types may be used depending upon the nature of the supporting surface, for example: a headed through-bolt or stud-welded bolt may be used where the supporting surface is the flange of a steel runway beam; and an anchor bolt may be embedded in a concrete supporting surface.
Two types of conventional connectors are described in U.S. Pat. No. 2,134,082 to Goodrich. In both cases, a clip is mounted to a bolt through a round hole nominally sized to suit the bolt diameter with clearance. Between the clip and supporting surface is a plate which abuts the outer face of the flange. In one case, the plate is rectangular having a diagonal slot through which the bolt passes. The rail flange may be laterally moved by tapping upon the transverse ends of the plate whereby the bolt engaging the diagonal slot forces the plate forwardly and rearwardly. The outer face of the flange, in transmitting lateral loads to the securing bolts, may bear upon the full forward face of the rectangular plate. In the second case described in U.S. Pat. No. 2,134,082, the abutting plate and clip have circular mutually registering holes. The plate has a symmetrical forward face of varying radial curvature centred about the hole in the plate such that rotation of the plate about the bolt results in a lateral shifting of the rail flange. In the second case, the outer face of the flange bears upon a small curved area on forward face of the curved plate. When the clip is securely clamped with the nut, the lateral loads from the rail are transmitted to the bolt mainly through friction between the forward portion of the clip and the top surface of the flange. Through vibration and impact due to the moving machinery, the nut often loosens and in the second case described, concentrated loads bear upon the forward face of the curved plate. These concentrated loads may exceed the bearing capacity of the curved plate or flange resulting in indentations which tend to act as stress concentrators in initiating fatigue failure. In addition, the rail and curved plate may wear excessively in the area of bearing necessitating replacement. In the first case, the rectangular plate more evenly distributes the bearing stresses, however the space required to accommodate the rectangular plate between its extreme forward and rearward positions may be considered excessive in some applications.
More compact connectors are described in U.S. Pat. No. 1,470,090 to Manning and U.S. Pat. No. 3,934,800 to Molyneux. The clips of these connectors have an oversized central hole with a countersunken circular upper portion which accommodates a circular washer. The washer has an offset eccentric hole nominally sized to suit the bolt which passes through it. The clip has a forward portion which engages the top surface of the flange and has an abutting shoulder portion rearward of the forward portion to engage the outer surface of the flange. The abutting shoulder evenly distributes the lateral bearing loads from the rail. Rotation of the washer about the bolt in a loose condition causes the circular peripheral surface of the washer to slide upon the interior circular surface of the countersunken upper portion of the clip's central hole. Therefore, rotation of the washer causes the clip to shift forwardly and rearwardly to align the rail flange due to the eccentricity of the hole in the washer. Such circular eccentric washers are relatively easy to manufacture, however, considerable mechanical disadvantages result through their use. When such a clip is at its rearwardmost or at its forwardmost position, and the distance between the eccentric hole and the forward portion of the clip is at a minimum or maximum, rotation of the washer through a fixed angular increment results in a relatively large lateral movement of the clip. In these positions therefore, the connector has poor sensitivity since a small rotation results in a large displacement of the clip. The mechanical advantage is also poor in that a large torque needs to be applied in order to displace the clip and rail against a given resisting force. When the clip is at an intermediate position, rotation of the washer through the same fixed angular increment results in a relatively small lateral movement of the clip. In this position the connector has increased sensitivity since a relatively large rotation of the washer is required to displace the clip a given amount, but the torque needed to displace the clip and rail against a given resisting force is smaller.
The alignment operation using such conventional connectors is complicated by the washer's varying sensitivity and responsiveness regarding lateral movement and angular position. The varying effort required and sensitivity make the alignment operation one of trial and error for all practical purposes since it is difficult to predict the correspondence between the torque applied and the resulting lateral movement
A further problem with these connectors is that it is easy to install them in an incorrect orientation in which tightening of a nut on the bolt rotates the washer in a sense which tends to loosen the clip.
It is desirable therefor, to provide a connector which has a sufficient bearing area to eliminate the problems associated with concentrated loads and that is easy to install and adjust correctly.